The present invention relates to engine component trend monitoring and, in particular, to aircraft and helicopter engine component trend monitoring for maintenance management. The invention further relates to a an engine maintenance monitoring display.
It is well known that aircraft turbine engines have to be regularly overhauled and inspected to prevent problems during engine operation. One particular type of inspection, known as Hot Section Inspection (HSI), is typically performed on a turbine engine after a predetermined period of time to assess the wear and tear on specific engine components. Hot section inspections are expensive in terms of the cost of manpower involved, since these inspections typically require that the engine be partially disassembled to view the particular parts under inspection. They are also expensive because they require the particular aircraft involved to be taken out of service. Another type of maintenance that may be required at any time during aircraft service is the replacement of critical components that have a declared life limit. Life limits are typically specified in terms of a maximum number of cycles or hours. Another type of engine maintenance which must be performed on turbine aircraft engines is what is known as Overhauls. Overhauls involve the aircraft and engine being taken out of service so as to permit the inspection, the repair or the replacement of all engine components. This type of maintenance is particularly expensive and can cost as much as 70% of the original cost of the engine, depending on the engine type and exactly what components need to be overhauled. For helicopter engines, most manufacturer maintenance concept requires that the basic time between overhaul (TBO) be performed at about the three-thousand hour service mark. With relevant supporting data and the help of the engine manufacturer, fleet operators can obtain extension from the published basic TBO or adhere to a xe2x80x9con-conditionxe2x80x9d engine overhaul program.
The problem that arises with most aircraft turbine engines is that the engines are exposed to different levels of wear during their operational service. For example, the helicopter engine may be exposed to higher levels of wear if there are a large number of take-offs and landings during a given mission. During each take-off, the engine must be spooled up to its lift-off rotational velocity and when the helicopter lands, the engine must be spooled back down to a low speed so that the helicopter can loiter on the ground, or the engine is spooled down to shut off. Each one of these take-offs and landings represents a single cycling of the engine, and for an in-service helicopter, there may be several take-offs and landings during a given mission. The greater the number of cycles per mission, the greater the wear on the engine components.
Another element which further adds wear to the engine components is the manner in which the engines are throttled-up and down during each one of these cycles. Pilots often have different styles of flying, due to different weather conditions or personal experience and may sometimes use the throttle controllers in a manner which places higher levels of stress on the engine components than what may be ordinarily expected. For example, a helicopter pilot who is flying on a tight mission schedule, may spool up the engine faster so as to get off the ground sooner. That same pilot may also spool down the engine faster so as to land more quickly, loiter on the ground at a high engine rotational velocity and then quickly spool the engine back up to become airborne again more quickly. Operational usage of the engine under these circumstances places even higher stresses on the engine components than would normally be expected. This reduces the amount of in-service time before the engine components require either a hot section inspection, a critical part replacement, or a complete overhaul.
Since different aircraft fleets are exposed to different levels of operational stress, the actual wear on engines from one fleet to another may vary considerably. Likewise, different aircraft within a fleet may be subjected to different levels of operational stress, and the actual wear on engines from one aircraft to another may vary considerably.
Aircraft engine maintenance is a significant cost in operating any aircraft-based service. Poor financial planning for the costs of inspections, part replacements, engine overhauls, etc., cannot be tolerated. Various maintenance plans have therefore evolved in the aircraft maintenance industry to provide aircraft-based service operators with a schedule of fixed costs for engine maintenance over a period of a number of years. Since engine maintenance plans, e.g. a guaranteed financial protection plan (GFPP), are standardized, some aircraft fleets with lesser degrees of actual wear may require maintenance too soon, while other fleets with greater degrees of wear may require maintenance sooner than anticipated.
The standardization of aircraft engine maintenance is based on a rough, although sometimes sophisticated, estimate of expected engine component and aircraft usage in a fleet for the period of time of the maintenance plan. In the case of an established operation, the plan can thus be based on a prediction of engine component wear and usage by analyzing the history of engine usage and/or aircraft usage as well as the particular maintenance requirements of the engines. Flight log books can be analyzed to determine factors such as altitudes reached, fuel consumption, the number of engine cycles (i.e. take-offs and landings, as well as engine spooling downs), and hours in flight. In the case of a new operation or a new engine, the standardization of the maintenance plan can even be more difficult and thus it may have a larger margin of error. As a result, it becomes a difficult task for an engine maintenance service provider to determine whether a rate for maintenance plan is being fairly applied to each of its customers. It also becomes a difficult task for maintenance managers of aircraft fleets to determine if the engines in the fleet are being flown in proper compliance with a maintenance plan. Furthermore, it becomes a difficult task for aircraft maintenance managers to accurately predict and optimize the dates for shop visits or predict the costs inherent with shop visits.
The net result of following such a maintenance plan according to the prior art is that aircraft-based service operators who use and operate their aircraft with care and under favorable conditions actually pay more than they should. Thus there is no incentive in the maintenance plan to manage the operation of an aircraft or fleet to reduce or control engine component usage.
Accordingly, it is an object of the present invention to provide a method for monitoring engine usage, and determine time remaining until hot section inspections, critical component replacements, and engine overhauls. According a first broad aspect of the invention, this object is provided by a display which allows for a comparative indication of engine component usage relative to maximum recommended usage.
It is another object of the invention to provide a method for monitoring engine usage to predict shop visit dates and maintenance plan costs.
It is another object of the present invention to provide a method for monitoring engine usage to determine a suggestion as to better use of an aircraft or particular aircraft within a fleet of aircraft to control engine wear on aircraft having higher levels of wear.
It is a further object of the present invention to provide a method for monitoring engine usage to determine compliance with an engine maintenance plan, and to produce reports pertaining to engine maintenance plan compliance.
According to a first aspect of the invention, there is provided a method of monitoring operation of at least one engine comprising establishing a time schedule of planned maintenance activities for the engine based on an expected use of the engine, monitoring operational parameters for the engine during use, analyzing the operational parameters to predict when the planned maintenance activities should be performed, providing an indication of whether a usage of the engine necessitates maintenance ahead of schedule. The maintenance plan schedule can be based on the most probable scenario under the conditions of proposed use of the engine. By providing an indication as to whether the actual operation of the engine over time is compliant with the maintenance plan, the engine operator can manage engine operation accordingly. The aircraft or fleet profile information used to prepare a maintenance plan may include the geographical location of the operation of the aircraft engine, the flying hours per year, the length of flights, the desired time between overhauls (TBO) and the time between hot section inspections (HSI) requested by the aircraft operator, as well as information on the operator""s background or history if available. The intended aspects to be included in the maintenance plan are the following scheduled event: overhaul (O/H); hot section inspection (HSI); low cycle fatigue (LCF), namely the replacement of parts after normal service life; and basic unplanned removal (BUR) of parts that require replacement before their normal service life (these events are not fixed in time, but based on probability of the events occurring, the cost is factored into the maintenance plan).
Preferably, the method further comprises steps of setting a schedule of charges corresponding to the time schedule of planned maintenance activities, and of adjusting, if necessary, the schedule of charges if the usage of the engine necessitates maintenance ahead of schedule. Maintenance can take the form of inspections, cleanings, part conditionings and part replacements. Preferably, the indication of whether the usage of the engine necessitates maintenance ahead of schedule comprises providing an indication of the predicted date and the planned date for the maintenance activity.
According to the above objects, the invention provides a method for accurately calculating a time remaining until service of an engine component, comprising the steps of:
(i) recording operational parameters including hours in use, and including at least one of temperature and rotational speed for said engine component;
(ii) analyzing said operational parameters recorded;
(iii) determining an engine usage value and an engine usage rate value for said component based on said analyzing; and
(iv) comparing said engine usage value and said engine usage rate value with reference values to predict a time when service of said engine component will be required.
The operational parameters may be any engine parameters which can be used to determine xe2x80x9cwear and tearxe2x80x9d on the engine component. Typically, such parameters include at least temperature and rotational speed over time. Torque is also a useful parameter and is used to verify engine performance. In both turbine and piston engines, fuel consumption is an additional useful parameter.
The engine usage value provides an indication of how much of the service life of the engine has been used up. The engine usage rate value may be an average usage per unit time or per unit activitity, such as cycles, missions, trips or distance travelled. The rate may be based on a full history since the beginning of recording, eg. since the last maintenance, or over a more recent shorter time period. The xe2x80x9cpredicted service timexe2x80x9d is generally an indication of the time when servicing is required under a warranty program, or an indication of the number of nominal flights, cycles or missions before the next servicing will be required under warranty.
Preferably, the predicted service time is calculated for a plurality of engine components of an aircraft, and the method further comprises a step of providing a display of the predicted service time for the plurality of engine components including an indication of a maintenance plan service time and a total engine component usage time. In this way, an operator compares predicted service time among engine components with the maintenance plan service time to determine which engine component will require maintenance first, and assesses whether the predicted service time is ahead or behind the maintenance plan service time. The display or printout obtained indicates how much time is left before servicing will be required, as well as information as to whether engine usage is balanced and above or below normal or expected levels. The operator may adjust how the aircraft is used to compensate for any imbalance among engine component usage and may temper engine component usage if it appears excessive. The operator""s objective is to make sure that maintenance is performed only when required by the maintenance plan (and not necessarily sooner than need be), and that all engines or engine components fall due for maintenance as close as possible in time.
When maintaining a multi-engine aircraft, certain engines may require maintenance before others, and the goal is to balance engine usage so that all engines require maintenance at the same time. Likewise, if a small fleet is to be brought in for maintenance at the same time, the goal is to balance usage of various aircraft.
According to the above objects, the invention also provides a method for managing usage of an aircraft in a fleet of aircraft, comprising the steps of:
(i) recording operational parameters including hours in use, and including at least one of temperature and rotational speed for each engine of said aircraft;
(ii) analyzing said operational parameters recorded;
(iii) determining an engine usage value and an engine usage rate value for said aircraft based on said step of analyzing;
(iv) comparing said engine usage value and said engine usage rate value with reference values to predict a time when service of said aircraft will be required; and
(v) managing aircraft usage based on said predicted service time.
According to the above objects, the invention also provides a processing system cooperating with a display system, wherein the display system is configured to display the estimated time until service for a plurality of engines simultaneously.
According to the above objects, the invention further provides a method for determining compliance of an engine with an engine warranty, the warranty defining a predetermined level of wear for an engine, comprising the steps of:
(i) counting the cycles per mission for at least one component of the engine;
(ii) weighting the cycles per mission based on wear and usage of the engine;
(iii) averaging the weighted cycles per mission over a total number of missions; and
(iv) comparing the average cycles per mission to a predetermined standard cycles per mission, wherein the engine is compliant with the warranty if the average cycles per mission are less than or equal to the predetermined cycles per mission, otherwise, the engine is not compliant with the warranty.